As a color image forming apparatus with an electrophotographic system, there are the apparatuses, for example, from those designed for office use such as a color printer or a color copier to those used in the commercial printing field, which are called desk-top publishing (DTP) and on-demand publishing. In this commercial printing field, preferably employed are those such as pre-press machines which are employed in the preparatory stages before preparing plates for mass-printing, and apparatues performing quick printing of a small lot such as several thousand prints to several ten thousand prints.
Incidentally, in commercial printing of color images, demanded are commercial photographs and background images exhibiting subtle tone and excellent granularity. In the electrophotographic method, specifications in recording density have been increased year after year because of the progress of an optical source such as laser, a LED or the like, and an optical system thereof, but problems concerning a photographic image and halftone granularity have been left over since no developing stability can be followed with respect to the dot diameter of color toner.
Further, also in the case of color reproduction, there was a problem such that corporate color and logo mark of each enterprise, and coloring of most of trademarks and products were not covered within the color reproduction range of printing standard color. In this way, one of the reasons is that no coverage within the color reproduction range leads to what each enterprise or association exercises its ingenuity in color to transmit a message to viewers via color tone. Accordingly, it is not rare that in the past, corporate color, logo mark, trademark or the like has been output by using a specific one called special color toner.
In such the way, since there is still a gap between the printing standard color and the human perceivable color gamut range, technology development to fill the foregoing gap is in progress in the field of displays such as a TV and the like so as to obtain reasonably comfortable color images to the sight. Specifically, the following Patent Documents 1 and 2 can be cited, but techniques disclosed in these documents remain at the level of conventional commercial printing, and color reproduction demanded in the present situation where digitalization is promoted has not been realized. For example, when preparing halftone images in which comfortable image quality is specifically desired, textured image quality feeling originated by area tone with dots is undeniable, whereby uniform image quality with no unevenness has been demanded. Further, since insufficient appearance of solidity is obtained when outputting photographic images, there are quite a few users feeling short on the images.
(Patent Document 1) Japanese Patent O.P.I. Publication No. 2005-315058
(Patent Document 2) Japanese Patent O.P.I. Publication No. 11-338190